A pain is coming? Uncertainty intensifies brain activity and influences perception

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 (Image: Pixabay CC0)
(Image: Pixabay CC0)
The perception of pain is a crucial signal that allows us to protect our body integrity. On the other hand, when a pain persists over time, the brain must learn to predict its evolution in order to limit the risk of injury.

A team of scientists from the Institute of Neuroscience of the UCLouvain (IoNS), Prof. André Mouraux and Dounia Mulders , FNRS research fellow, together with their colleagues Ben Seymour (University of Oxford, UK) and Flavia Mancini (University of Cambridge, UK) are trying to understand these prediction mechanisms.

Does a stronger painful stimulus lead to a higher response? "Not systematically, the brain does not carry out a simple passive reading of the pain", notes Dounia Mulders, because the expectations of the individual affect what he perceives.

The team subjected participants to sequences of thermal stimuli - either hot or cold - each sequence having distinct structures - majority of hot or cold stimuli, numerous hot-hot or cold-cold repetitions, numerous alternations of intensity, etc. These structures could thus be estimated by participants during the sequences. These structures could then be estimated by the participants during the sequences.

Result - Scientists have found that a high degree of uncertainty about the incoming stimulus leads to higher neuronal activity. In other words, when the subject knows with certainty what type of stimulus he or she will receive, brain activity is reduced. Why - Because the brain relies more on the anticipations made by the subject than on the stimulus that is actually applied.

The researchers also showed that uncertainty about future pain intensities plays a key role in learning their sequence structure (i.e., in what order, with what intensity, and at what rate the stimuli appear).

What is the interest of these results - They will allow, among other things, to help patients who suffer from chronic pain - it lasts in time, is variable and affects/will affect 20% of the population - by opening the door to new clinical studies. It is already known that pain can sometimes be perceived in the absence of any stimuli but only in the presence of expectations.

It is the understanding of the basis of these mechanisms that the researchers propose in this first study whose results are published in the prestigious journal Proceedings of the National Academy Sciences (PNAS).